In Global System for Mobile Communications (GSM) wireless networks, controllers in the Mobile Switching Center (MSC) coordinate the handover (sometimes referred to as handoff) of mobile users upon traveling from one cell or base station of the network to another cell of the network. Handover may also be performed to relieve the load on a particular base station. The handover is a communication transfer for a particular mobile user from one base station to another base station. There may be a transfer period during which the uplink and downlink communications to the mobile user are severed with the base station of the first cell and not yet established at the base station of the second cell.
In order to optimize the performance of the handoff and reduce the possible break in the link, it is important to maintain frequency accuracy and, if possible, maintain network wide synchronization at base transceiver stations in a wireless network. Previously network wide synchronization of base transceiver stations had been achieved by using free running very accurate crystal oscillators or timing operations that determine and compensate for distances between base station controllers and base transceiver stations at a base station. Free running oscillators present maintenance and stability issues, require the same equipment vendor for the base station controller and base transceiver stations, and require base transceiver stations to be associated with a single base station controller. Timing operations to compensate for distance are complex and expensive.
In public wireless networks, base stations may be equipped with Global Positioning System (GPS) receivers to provide a frequency and timing reference. The use of GPS receivers does not solve the problem since it is not always possible to receive the required radio signals from a GPS satellite or retransmitted signal, especially for private wireless systems that are indoors. Moreover, the cost of these GPS receivers is justified in public wireless networks where a large number of calls are supported and the cost of the base station is very high. Private wireless networks may handle only a small number of calls and need to be much more cost effective, thus making a GPS receiver cost prohibitive. Even when a synchronized clock is provided to each base station, internal clock signals in each base station derived from the synchronized clock must also be synchronized so that time differences between internal clocks of different base stations is not too great to hinder providing a synchronized handoff. Therefore, it is desirable to provide effective handoff synchronization, especially for private wireless networks. In addition by synchronizing the base station radio interfaces it is possible to improve the voice quality of the network.